1. Field of Invention
This invention relates to a compression coupling and more particularly to a coupling for connecting a conduit, such as an unthreaded metal pipe or a plastic pipe, to a valve, meter, or the like where a portion of the conduit positioned within the coupling is reinforced by an insert that remains frictionally engaged to the conduit to prevent pullout of the conduit and insert from the fitting.
2. Description of the Prior Art
Compression couplings are well known in the art for connecting flexible conduits or plastic pipe and unthreaded metal pipe to a main fluid distribution line or to the fitting of a valve body or a meter, such as a customer gas or water meter. In recent years, it has become the common practice to connect nonmetallic pipes, such as pipes fabricated of polyvinyl chloride (PVC), polyethylene (PE), polybutylene (PB) and the like to metallic pipes, valves, meters, etc. by compression couplings for the distribution of gas and water. A typical coupling for connecting nonmetallic, plastic pipes to fittings or metal pipes is disclosed in U.S. Pat. No. 3,596,933.
A typical compression coupling is disclosed in U.S. Pat. No. 3,784,236 and includes a coupling nut assembly having a compression nut threadedly engageable with a tubular fitting. Threadedly advancing the nut on the fitting compresses an elastomeric sealing gasket into annular compressing contact with a flexible conduit, such as a plastic pipe. By compressing the annular gasket against the flexible conduit, the conduit is retained in the coupling nut assembly. This arrangement also provides a seal between the coupling nut assembly and the plastic conduit.
In order to prevent crimping or breaking of the flexible conduit at its connection to the coupling nut assembly, it is the common practice to reinforce the flexible tubing by a stiffener sleeve or reinforcing insert positioned within the flexible conduit in underlying relation with the compression nut. With this arrangement when the nut is tightened down on the fitting, the stiffener reinforces the flexible conduit to prevent distortion of the flexible conduit. Examples of stiffener sleeves or reinforcing inserts are disclosed in the following U.S. Pat. Nos. 3,404,905; 3,428,339; 3,596,933; 3,685,860; 3,784,236; 3,834,742; and 4,032,177. For the stiffener sleeve to remain effective, it must be retained within the fitting in underlying relation with the portion of the flexible conduit positioned oppositely of the sealing gasket. It is at this point along the flexible conduit where tightening of the nut on the fitting applies pressure upon the flexible conduit.
A common problem encountered with couplings for plastic pipes utilizing a stiffener sleeve is pullout of the stiffener sleeve and conduit through the annular sealing gasket and out of the coupling fitting. In addition if relative movement is permitted between the stiffener sleeve and the conduit, the stiffener sleeve may be pulled out of the coupling or displaced from reinforcing position within the coupling. This reduces the length or stab depth of the flexible conduit in the coupling. The stab depth of the flexible conduit in the coupling should be sufficient to permit limited movement of the conduit relative to the coupling so that a sufficient length of the conduit remains in the coupling and is reinforced by the sleeve.
While it has been suggested by the prior art devices to reinforce a flexible conduit by a stiffener element within a coupling assembly joining the flexible conduit to another pipe or fixture, the prior art devices rely principally upon retaining the conduit in the fitting by tightening the compressive nut to compress the sealing gasket on the flexible conduit. Such arrangements have not proved satisfactory in preventing pullout of the conduit and to the stiffener element from the coupling fitting. Also if the sealing gasket should loose its resilient properties, then the conduit will not be sufficiently compressed to resist pullout of the conduit and the stiffener from the fitting.
Therefore, there is need to provide in a compression-type coupling an arrangement for retaining both the stiffener element and the conduit locked within the fitting to resist pullout of the conduit and the stiffener element.